A wind turbine generally comprises a tower, a nacelle, at least one blade and a yaw bearing arranged between the tower and the nacelle. A high voltage cable is drawn from a generator arranged in the nacelle, down to the ground through the interior space of the tower. Generally, the cable has a diameter of 60-110 mm. This high voltage cable is not the only cable extending from the nacelle through the interior of the tower, but also other additional cables, such as signal cables or the like, are extending in the same manner through the tower. Normally, these cables are mounted on the outer surface of the high voltage cable. To avoid disturbances from the high voltage cable, the latter must be provided with an outer shielding, thereby increasing its thickness, weight and cost.
In operation, the nacelle is turned around the yaw bearing in order for the blades to be correctly oriented towards the wind. This turning is transferred to the cables, thereby twisting or turning the same. In order to allow for this twisting, the cables must have a free length, which is hanging centrally through the upper section of the tower. Along the lower sections of the tower, the cables are fixed to the inner wall of the tower. Along the wall, the additional cables and the high voltage cable are separated. Thus, the twisting is generally restricted to the free length of the cables along the upper section of the tower only.
Normally, the nacelle is allowed to be turned about five turns before it must be re-turned to its original position in order to avoid any damages to the cables.
Due to the extra shielding of the high voltage cable, which is required for avoiding disturbances on the additional cables arranged in the tower, the high voltage cable becomes expensive and heavy.
Additionally, all cables must be made with an extra length in order to allow for the twisting due to the turning of the nacelle, which additionally adds to the weight and cost of the cables.
GB 2 167 612 discloses a wind-turbine generator system having a nacelle-mounted generator provided with a slip ring assembly. The power cable from the generator is extending from the nacelle to the tower via the slip ring.